1. Field of the Invention
The present invention relates to a traffic management system with overload control functions for use in a telecommunications system, and more particularly, to a traffic management system which controls overload in call handling process in high-traffic conditions.
2. Description of the Related Art
In telecommunications systems, too many calls concentrated in a particular switching station or communications channel would cause an overload, and it could drive the network system into an abnormal condition where any new call requests from subscribers cannot be accepted; or the system is congested. Once such congestion has occurred, some impatient subscribers will repeat calling over and over until the connection is reached. Such subscribers' behavior will further increase the frequency of call handling processes executed in switching equipment, which, however, would mostly end up in vain. This leads to significant performance degradation in call connection services, and therefore, appropriate traffic management and congestion control are necessary so that the system will keep the quality grade required in telecommunications services.
FIG. 35 is a block diagram showing a telecommunications system where mobile communications networks are connected to a switching station of a general public telephone network. To provide mobile communication services in different geographical locations, the system comprises a plurality of radio port coverage areas (or cell, in cellular radio terminology) CI1 to CI3, which are served by base transceiver stations (BTSs) 91 to 93, respectively. Mobile stations (MSs) are distributed in those cells CI1 to CI3. The BTSs 91 to 93 are under the control of base station controllers (BSCs) 81 and 82, which are connected to a switching station 400 serving as a gateway to fixed public networks via digital trunks (DTs) 50a to 50d which monitor trunk circuit signals. The switching station 400 comprises a call processor (CPR) 401 and a main processor (MPR) 402. Further detailed explanation will not be presented here, since FIG. 35 is only for the purpose of showing the ideas of traffic condition in a mobile radio system. The distribution of active mobile stations is not uniform. FIG. 35 indicates this irregularity of distribution by different densities of mobile stations as illustrated in each coverage area CI1, CI2, or CI3. That is, the coverage area CI2 including the largest number of mobile stations is considered to be in a high-traffic condition.
FIG. 36 shows the load distribution in call handling processes performed by the CPR 401 with respect to the BSCs 81 and 83. Because the BSC 82 suffered from much heavier traffic than the BSC 81 due to the high population in the coverage area C12, most of its processor performance is spent for call handling of the BSC 82.
The first-mentioned network congestion sometimes occurs in such a situation that some disaster struck a certain region in a country and people in other distant areas are anxious about their friends or relatives living in that region. When an extraordinary increase of network traffic is observed in a particular area, it will be necessary to restrict the calls entering to the network to avoid congestion.
FIG. 37 is a conceptual view of a conventional call restriction method to restrict incoming calls to a telecommunications network system.
[S1] Call setup requests from mobile stations reach the CPR 401 via the BSC 82 and accepted by a call handling process 401a that is integrated therein.
[S2] The call handling process 401a inquires of a call restriction process 401b, another integral part of the CPR 401, whether any level of call restriction should be applied or not. The call restriction process 401b always monitors the traffic conditions by performing a central controller (CC) usage rate analysis 401c and transaction rate analysis 401d, and it responds to the inquiry from the call handling process 401a based on those analyses.
[S3] When the call restriction process 401b decided to execute some call restriction, it notifies the call handling process 401a that an n-percent call restriction should be applied. This n-percent call restriction means that the call handling process 401a will reject n-percent of call requests while accepting the rest of them. When a 50 percent restriction, for example, is effective, one of two calls will be connected and the other will not be connected.
[S4] Upon receipt of the notification, the call handling process 401a applies the n-percent call restriction to all the BSCs under the control of the CPR 401. More specifically, in FIGS. 35 and 37, the CPR 401 conducts the n-percent call restriction with respect to the two BSCs 81 and 82.
As described above, the conventional call restriction method implemented in a CPR applies the same call restriction process equally to all BSCs connected to the CPR, without considering individual call processing load that may differ from BSC to BSC. The above conventional method, therefore, produces adverse side effects on the grade of total communication services since the call restriction process will also affect activities of other BSCs in low-traffic conditions.